An electric valve disclosed in, for example, Patent Document 1 is already known as an electric valve of this type.
FIG. 6 shows a main part of the electric valve according to the conventional example described above. An electric valve 2 according to the illustrated conventional example is provided with a valve main body 40 in which a valve chamber 40a, a valve seat 46a, and a valve port 46 continuous to the valve seat 46a are disposed and a valve body 14 changing the flow rate of a fluid flowing through the valve port 46 in accordance with the lift amount from the valve seat 46a. The valve body 14 is raised and lowered to come into contact with and be separated from the valve seat 46a by a screw feed-type raising and lowering drive mechanism including a screw pipe (also referred to as a guide bush) in which a male screw portion is disposed, a valve stem holder in which a female screw portion is disposed, a stepping motor, and so on as described in, for example, Patent Document 1.
The valve body 14 has a seating surface portion 14a that includes an inverted truncated cone surface attached to the valve seat 46a and a curved surface portion 14b that is continuous to the lower side (tip side) of the seating surface portion 14a to change the flow rate of the fluid flowing through the valve port 46 in accordance with the lift amount. The curved surface portion 14b has an inverted truncated cone-shaped tapered surface portion (upper-side tapered surface portion 14ba and lower-side tapered surface portion 14bb) that has a plurality of stages (two stages herein), and the tapered surface portion has a control angle (crossing angle with a line parallel to a central axis O of the valve body 14) increasing in stages toward the tip. An ellipsoidal curved surface portion (ellipsoidal surface portion) and the like that have an outer peripheral surface increasingly bent (having a curvature increasing) in a gradual manner toward the tip are also known as the curved surface portion 14b. 
The valve port 46 has a narrowest portion 46s that includes a cylindrical surface continuous to the valve seat 46a and a diameter-enlarged portion 46b that includes a truncated cone surface which is continuous to the lower side of the narrowest portion 46s and has an inner diameter increasing toward the lower side.